vb-c++-connection

c++ dll has exported funtion call such as:
void AccessUnknownBuf(char** cbuffer, int sizeofbuf);
VB does not know about the size of cbuffer beforehand. It has to get the cbuffer and its size from dll. How VB can do this?. somehow it should be accessing dll's memory area...?. seconldy, how to allocate more than 40000 bytes for character string type?.
dim s as string*50000 does not work.

I dont think so. You are calling a function in a C++ dll and all you can get is the return type of the function or any pointer that you provide are having some data and the second option requires you to have the buffer in VB and pass that to C++ dll.